I misunderstood your suggestion originally. To me KDE is a big
monolithic thing, a behemoth the parts of which are not to be trifled
with by me. That said the problem (at least initially) is kmix. I did an
emerge -C kmix from the console and then started KDE. All microphone
settings appear to be OK.

Good to see my suspicions were correct. =:^) As for kde being big/
monolithic, yeah, that's an easy enough thought pattern to get into. But
it doesn't tend to help troubleshooting, and it's useful to remember that
there's a bunch of different developers each with their individual
thoughts and ideas working on kde too, sometimes. That's actually the
bit I have more trouble with, as it's very easy to take one kde-dev's
thoughts on something and pin them on kde as a whole, but it doesn't
necessarily work that way.

The next tests will be to exit KDE, come back in again, make sure things
are ok, maybe emerge kmix again, see if it's messed up again, etc. I'll
do that later today after the market closes. Right now I'm in the middle
of a bunch of trades.

AFAIK there's an option somewhere, that sets whether kmix resets the
volume on kde startup, or not. But as I said, it has been awhile since I
had it installed, and of course it's possible they changed it along the
line, too, which might explain why it started working differently for you.

QUESTION: Might you be able to suggest any other Open Source mixer to
replace kmix? I find I need a desktop mixer due to my work in VMs all
day long where every app and every machine has different volume levels.

Personally, alsamixer has worked well for me, for years. I can run it in
a konsole window when in kde, or from a VT when I'm not in X, which is
nice, and I actually find it clearer to deal with than kmix in some ways,
tho I liked kmix for its ability to have one (configurable) control set
as master, and being able to just pop that up from the tray, when
needed. But whenever I want to actually see what controls are available
and change the more complex options or adjust more than one channel, I
tend to prefer alsamixer.
Since I like alsamixer, it works equally well in a VT or a terminal
window, and it tends to be installed wherever alsa is used, which is
pretty much everywhere on Linux, I really haven't had much need to go
looking for anything else. Of course I know about kmix as part of kde,
but other than that, I haven't needed to look, so I haven't.

I recently came across alsamixergui which sounds like it might be a
replacement for kmix. I was thinking of installing it, but there are
dependencies on gnome libraries which I tend to avoid on mhy KDE
systems. If Kmix is causing problems for you though, you could look into
alsamixergui I guess.